The objective of this study is to ascertain whether pinocytosis provides macrophages with a means of utilization of materials present in serum or cells for augmentation or modification of their antibacterial capabilities. The approach will be to pretreat cultivated macrophages with substances stimulatory or inhibitory to pinocytosis in the presence and absence of sera, components of polymorphonuclear leukocytes or platelets and assay for intracellular inactivation of Listeria monocytogenes and Staphylococcus aureus. The rates of pinocytosis of horseradish peroxidase by macrophages in different states of activation will be compared with their ability to utilize exogenous serum or cell factors for bacterial inactivation. It will also be determined whether the heightened levels of bacteriostatic activity exhibited by macrophages activated through immunologic means in vitro is associated with stimulation of pinocytic utilization of factors present in serum.